Method and system for scene change detection in a video encoder

Abstract

Described herein is a method and system for rate estimation in a video encoder. The method and system use a motion estimation metric to determine the position of a scene change. The average of the motion estimation metric is computed for a set of pictures. When change in the motion estimation metric average exceeds a threshold, a scene change is declared. Declaration of a scene change prior to video encoding enables a corresponding bit allocation that can preserve perceptual quality.

1 . A method for detecting a scene change, said method comprising: 
 measuring differences between a first picture and a second picture;    measuring differences between the second picture and a third picture;    measuring the deviation between the measured differences between the first picture and the second picture, and the measured differences between the second picture and third picture; and    declaring a scene change wherein the measured deviation exceeds a predetermined threshold.    
     
     
         2 . The method of  claim 1 , wherein measuring the differences between the first picture and the second picture further comprises: 
 determining a first set of motion estimation metrics for the first picture and the second picture.    
     
     
         3 . The method of  claim 2 , wherein measuring the differences between the second picture and the third picture further comprises: 
 determining a second set of motion estimation metrics for the second picture and the third picture.    
     
     
         4 . The method of  claim 3 , wherein measuring the deviation between the measured differences further comprises: 
 calculating a difference between the first set of motion estimation metrics and the second set of motion estimation metrics.    
     
     
         5 . The method of  claim 3 , wherein determining the first set of motion estimation metrics further comprises: 
 generating a sum of absolute differences for each macroblock in the first picture or second picture.    
     
     
         6 . The method of  claim 5 , further comprising: 
 averaging the sums of absolute differences for each of the macroblocks in the first picture or second picture.    
     
     
         7 . A method for scene change detection in a video encoder, said method comprising: 
 determining a set of motion estimation metrics for a set of pictures;    calculating a difference in the motion estimation metrics over time; and    declaring a scene change where the difference exceeds a predetermined threshold.    
     
     
         8 . The method of  claim 7 , wherein a motion estimation metric for a current picture is based on a previous picture.  
     
     
         9 . The method of  claim 7 , wherein determining a set of motion estimation metrics further comprises: 
 generating a sum of absolute difference for each macroblock in a picture in the set of pictures.    
     
     
         10 . The method of  claim 7 , wherein the method further comprises: 
 allocating a larger number of bits to a picture encoded after the scene change.    
     
     
         11 . The method of  claim 7 , wherein a current picture is associated with a motion estimation metric based on a previous picture and a motion estimation metric based on a future picture.  
     
     
         12 . The method of  claim 11 , wherein the method further comprises: 
 adjusting the scene change based on the difference between the motion estimation metric based on the previous picture and the motion estimation metric based on the future picture.    
     
     
         13 . A system for rate estimation in a video encoder, said method comprising: 
 a motion estimator for: 
 determining differences between a first picture and a second picture; and  
 determining differences between a second picture and a third picture;  
   a differentiator for measuring the deviation between the measured differences between the first picture and the second picture, and the measured differences between the second picture and third picture; and    a peak detector for declaring a scene change wherein the measured deviation exceeds a predetermined threshold.    
     
     
         14 . The system of  claim 13 , wherein a set of motion estimation metrics comprises the measured differences between the first picture and the second picture and the measured differences between the second picture and the third picture.  
     
     
         15 . The system of  claim 13 , wherein the motion estimator further comprises: 
 a search engine for generating a sum of absolute difference for each macroblock in a picture; and    a SAD averager for averaging the sums of absolute difference for each macroblock in the picture, thereby producing a motion estimation metric in the set of motion estimation metrics.    
     
     
         16 . The system of  claim 13 , wherein the system further comprises: 
 a rate controller for allocating a larger number of bits to a picture encoded after the scene change.    
     
     
         17 . The system of  claim 13 , wherein a current picture is associated with a motion estimation metric based on a previous picture and a motion estimation metric based on a future picture.  
     
     
         18 . The system of  claim 17 , wherein the system further comprises: 
 a bidirectional picture sorter for adjusting the scene change based on the difference between the motion estimation metric based on the previous picture and the motion estimation metric based on the future picture.    
     
     
         19 . A system comprising: 
 an integrated circuit for determining a difference in a set of motion estimation metrics and declaring a scene change where the difference exceeds a threshold, wherein one motion estimation metric in the set of motion estimation metrics corresponds to one pictures.    
     
     
         20 . The system of  claim 19 , wherein a motion estimation metric for a current picture is based on a previous picture.  
     
     
         21 . The system of  claim 19 , wherein a motion estimation metric in the set of motion estimation metrics is an average of a sum of absolute difference.  
     
     
         22 . The system of  claim 19 , wherein the integrated circuit further allocates a larger number of bits to a picture encoded after the scene change.  
     
     
         23 . The system of  claim 19 , wherein a current picture is associated with a first metric and a second metric, wherein the first metric is a motion estimation metric based on a previous picture and the second metric is a motion estimation metric based on a future picture.  
     
     
         24 . The system of  claim 19 , wherein the integrated circuit further adjusts the scene change based on the difference between the first metric and the second metric.